1. Field of the Invention
The present invention relates generally to electrical wiring devices, and particularly to power control wiring devices such as dimmer and fan speed control devices.
2. Technical Background
In most residences, a simple ON/OFF switch may be the primary way people control lighting fixtures or air-circulating fan fixtures. One obvious drawback to using simple ON/OFF switches to control these devices is experienced when it comes time to pay the electric bill—a given light (or fan) is either ON or OFF—a simple switch is thus unable to vary the amount of light (and hence the amount of power consumed). Stated differently, by controlling light intensity or fan speed in accordance with needed or desired parameters, electricity usage is reduced, saving money and natural resources. In accordance with the present invention, therefore, a power control device refers to an electrical control device that may be employed to adjust the amount of current delivered to any variable electrical load, such as a light or motor. The adjustment is achieved by sliding a lever or rotating a dial.
When the electric load is a lighting device, the power control device is commonly referred to as a dimmer. For example, when a light is dimmed 25%, a dimmer saves about 20% of the electricity required. When dimmed by 50%, it saves 40% of the electricity. Second, a dimmer greatly extends lamp life because it reduces strain on the filament. When dimmed 20%, a lamp lasts 4 times longer than it would at full power, and dimmed by 50%, it will last as much as 20 times longer. If the power control device is configured to control a motor, such as a fan motor, the power control device is configured to control a motor, such as a fan motor, the power control device is referred to as a motor speed control. Motor speed controllers are also used to control the speed of machinery, such as power tools, electrical drills, chair lifts, stationary machinery, and other such variable motor driven elements.
Power control devices are typically packaged in a wiring device form factor for installation in a wall outlet box. The wiring device may include one or more power control devices within the device housing. For example, wiring devices that are equipped with both fan motor and lighting control features are ubiquitous. The wiring device may include another power control device such as a switch, protective device, ground fault circuit interrupter (GFCI), arc fault circuit interrupter (AFCI), surge protective device (SPD), occupancy sensor, or receptacle. When a switch is included, it may be wired in series with the dimmer or fan speed control to allow the load to be switched ON or OFF. The conventional wiring device form factor provides a user accessible interface that includes one or more switch mechanisms such as buttons, levers, dials, slide switches, and other such input control mechanisms that permit a user to vary the power to a load or turn it ON/OFF.
Prior to device installation, wiring from the AC power source and wiring to the load(s) are disposed inside the outlet box. The outlet box is usually located proximate to the load being controlled. The device is installed by connecting the wiring inside the outlet box to the appropriate wiring device terminals disposed on the exterior of the wiring device. The power control wiring device is then inserted into the outlet box and attached to the outlet box using one or more fasteners. A cover plate is installed to complete the installation.
Turning now to so-called “green” issues, the public has developed an increased awareness of the impact that energy generation has on the environment. Moreover, as the economics of countries such as Brazil, India, China, etc. improve and develop, their need for energy resources increases accordingly. As such, the global demand for energy has risen sharply, while the supply of planet earth's resources remains fixed. In light of the pressures of supply and demand, the cost of energy resources will only increase. There is thus a need to use limited energy resources more wisely and more efficiently. More efficient light sources and electrical fixtures have been developed to replace the conventional incandescent lighting devices in response to this need. For example, compact fluorescent lights (CFL) and light emitting diode (LED) devices are far more efficient than conventional incandescent lights and thus provide homeowners/tenants with an acceptable level of service while using less energy and incurring lower costs. This may complicate matters somewhat since incandescent lights, fluorescent lights, MLV lighting, CFL devices and LED lighting may have different electrical operating characteristics.
Thus, one of the drawbacks of a conventional dimmer device is that it may not be compatible with all of the types of lighting devices currently available. The minimum range of adjustment of the dimmer may be fine for one type of light source but cause another type to flicker. The maximum range of adjustment of a conventional dimmer may satisfactorily limit the energy usage for one type of light source but not for another. Conventional fan motor controls have similar issues in that they are not compatible with all the various fan motors currently on the market.
Moreover, the typical user may want to adjust the operating range of his fan motor or dimmer in accordance with their personal needs and preferences. Some conventional dimmers and fan speed controls have calibration devices that allow the user to set the minimum range of adjustment or the maximum range of adjustment using a trim potentiometer, but not both. Conventional dimmers cannot calibrate both the high end and the low end because trim potentiometers are expensive and bulky; fitting in two potentiometers, one each for the high and low calibration is prohibitive from both a cost and space standpoint. Furthermore, trim potentiometers require large access holes through the device's heat sink and, thus, the effectiveness of the heat sink is diminished. Once again, using two trim pots is prohibitive, this time from a safety standpoint.
Accordingly, a need exists for a safe, cost-effective and economic power control device that lets the user calibrate the dimmer device to a variety of electrical loads over a wide range of power settings.